La réduction des émissions de polluants et la diminution de la consommation sont deux challenges fortement liés auxquels les constructeurs automobiles doivent faire face tout en maintenant les performances des moteurs. Les nouvelles stratégies telle que la réduction de la cylindrée associée à une optimisation de la boucle d'air (forte suralimentation et recirculation de gaz brûlés) possèdent ce potentiel. Cependant elles affectent la stabilité du moteur en favorisant les variations cycle à cycle (VCC) qui correspondent à une fluctuation de la combustion d'un cycle sur l'autre. L'objectif de cette thèse est de développer une méthodologie s'appuyant sur la Simulation aux Grandes Echelles (SGE) capable de prédire les VCC d'un moteur à allumage commandé. Les prédictions sont validées grâce à une base de données expérimentale conçue à l'IFP qui leur est dédiée. Une approche graduelle est employée : l'outil numérique est tout d'abord évalué sur une configuration simplifiée de moteur à piston sans combustion, puis appliqué à un moteur à allumage commandé entraîné pour valider la prédiction de l'aérodynamique interne. Sur cette dernière configuration le couplage avec le modèle de combustion DTFLES est rajouté pour simuler deux points de fonctionnement réactifs. Chacune de ces simulations intègre un ou plusieurs points de modélisation (les tétraèdres en maillage mobile, les modèles de choc et d'allumage, et la cinétique chimique) au préalable testés sur des configurations académiques. Ce travail de recherche montre que l'approche SGE, dans un contexte de calcul massivement parallèle, est un outil prometteur dans l'étude des VCC d'un moteur à allumage commandé de conception récente. / A major challenge for the development of internal combustion engines is to improve fuel economy and to reduce pollutant emissions while maintaining or enhancing engine performances. New strategies using downsizing with high levels of exhaust gas recirculation have this potential, but can impact on the combustion stability and trigger high cycle-to-cycle variations (CCV). The objective of this thesis is to set a methodology based on Large Eddy Simulation (LES) to study CCV of a Spark-Ignition (SI) engine. A gradual approach is used : the numerical tool is first evaluated on a motored axisymmetric piston-cylinder assembly, and then applied on a motored SI engine to validate the in-cylinder aerodynamic predictions. On this last configuration, the coupling with the turbulent combustion model DTFLES is added to simulate two operating points of the indirect injection engine mode. Each of these simulations takes into account one or several modeling key points (tetrahedra with moving mesh, the modelings of shock and ignition, and chemical kinetics) previously tested in academic configurations. This research work shows that LES approach, in the context of massively parallel computing, can be used to study the CCV of a realistic SI engine.

L'amélioration des moteurs à allumage commandé représente un défi de première importance pour les ingénieurs afin de produire plus d'énergie, de consommer moins de matière première et de réduire les émissions polluantes. Les nouvelles technologies apparues ces dernières années amènent les moteurs de plus en plus proches de leurs limites de fonctionnement, favorisant ainsi des phénomènes néfastes qui doivent être contrôlés. Parmi ces phénomènes, les variations cycle-à-cycle (VCC) doivent être minimisées pour garder une performance optimale et éviter une dégradation rapide du moteur. La Simulation aux Grandes Echelles (SGE) est un outil prometteur afin de prédire numériquement les niveaux de variabilités obtenues lors du design d'un moteur (limitant ainsi les coûteuses campagnes de mesures expérimentales). Ce manuscrit s'est attaché à développer une méthodologie numérique pour la prédiction des variabilités cycliques, à simuler un nombre suffisant de cycles pour pouvoir estimer les niveaux de VCC et à valider les résultats obtenus par rapport aux résultats expérimentaux. La SGE semble capter les points de fonctionnements stable et instable étudiés. Les sources qui provoquent ces VCC ont aussi été analysées et une modification du fonctionnement du moteur a été proposée afin de réduire les VCC. / The improvement of the spark ignition engines is a major challenge for engineers in order to produce more energy, to minimize fuel consumption and to reduce the pollutant emissions. The new technologies which appear in the last years bring the engines closer to their stability limit while increasing various unwanted phenomena. Among these phenomena, cycle-to-cycle variation (CCV) need to be minimized in order to keep the performances as high as possible and avoid damages on the engines. Large Eddy Simulation (LES), which is a very promising tool in order to predict the level of CCV of a given engine, has been used in the present document to simulate a mono-cylinder spark ignition engine. The present document presented a numerical methodology for the prediction of CCV, numerous engine cycles were simulated by LES in order to validate the results in comparison to the experimental findings. The LES seems to be able to capture stable and instable (in terms of CCV) operating points of the engine. In addition, the sources of CCV were also analyzed and a modification of the engine has been proposed to reduce CCV.

O presente trabalho aborda o gerenciamento eletrônico de motores de combustão interna flex, com foco no desenvolvimento de uma estratégia de controle do avanço de ignição em função da ocorrência de combustão anormal conhecida como detonação, para se maximizar o torque de saída do motor. Primeiramente, é desenvolvido um método para a medição da composição de combustível e correção dos parâmetros de tempo de injeção e avanço de ignição, através de um sensor de composição de combustível. Tais parâmetros são definidos através de mapas que trabalham como um sistema de malha aberta. Em seguida, é desenvolvido um método para a leitura e detecção de detonação, em que são estudadas as particularidades do fenômeno para diferentes composições de combustível e a sua relação com a variação da temperatura do gás de escape e torque de saída do motor. Através do método de detecção e do estudo do fenômeno, é desenvolvido uma estratégia para controle do avanço de ignição em função da ocorrência da detonação. Esta abordagem permite ao sistema aumentar o avanço quando não há ocorrência de detonação, mas este avanço adicional é cancelado quando ocorre detonação. O gerenciamento do motor é realizado através de uma ECU de desenvolvimento modelo Flex-ECU, as estratégias de gerenciamento são desenvolvidos através da plataforma ASCET e a aquisição de dados e calibração de parâmetros são executados em uma ferramenta de medição e calibração. Os benefícios que o controle do avanço de ignição traz ao torque do motor são analisados e discutidos em função da rotação e da composição de combustível utilizado. / The present investigation explores the electronic management of internal combustion engines flex fuel, in which the focus is the development of a strategy for the spark advance angle as function of the abnormal combustion occurrence known ad Knock, in order to maximize the output torque. First, a method is developed for measuring the fuel composition and correction of the injection time and spark advance angle parameters through a fuel composition sensor. This parameter is defined through maps that work as an open loop system. Then, a method for detection of knock is developed, the peculiarities of the phenomenon are studied for different fuel compositions and the relationship of the phenomenon with the variation of the exhaust gas temperature and the engine output torque. Through the method of detection and the study of the phenomenon, an algorithm is developed to control the spark advance angle due to the knock occurrence, in which the approach allows the system to increase the angle when there is no occurrence of knock, but this additional angle is reduced when knock is detected. Engine management is performed through a development ECU model Flex-ECU, management algorithms are developed through the ASCET platform and data acquisition and calibration of and parameters is performed through a measurement and calibration platform. The result that the spark advance angle control brings to the engine torque output is analyzed and discussed depending on the rotation and the fuel composition used.

O presente trabalho aborda o gerenciamento eletrônico de motores de combustão interna flex, com foco no desenvolvimento de uma estratégia de controle do avanço de ignição em função da ocorrência de combustão anormal conhecida como detonação, para se maximizar o torque de saída do motor. Primeiramente, é desenvolvido um método para a medição da composição de combustível e correção dos parâmetros de tempo de injeção e avanço de ignição, através de um sensor de composição de combustível. Tais parâmetros são definidos através de mapas que trabalham como um sistema de malha aberta. Em seguida, é desenvolvido um método para a leitura e detecção de detonação, em que são estudadas as particularidades do fenômeno para diferentes composições de combustível e a sua relação com a variação da temperatura do gás de escape e torque de saída do motor. Através do método de detecção e do estudo do fenômeno, é desenvolvido uma estratégia para controle do avanço de ignição em função da ocorrência da detonação. Esta abordagem permite ao sistema aumentar o avanço quando não há ocorrência de detonação, mas este avanço adicional é cancelado quando ocorre detonação. O gerenciamento do motor é realizado através de uma ECU de desenvolvimento modelo Flex-ECU, as estratégias de gerenciamento são desenvolvidos através da plataforma ASCET e a aquisição de dados e calibração de parâmetros são executados em uma ferramenta de medição e calibração. Os benefícios que o controle do avanço de ignição traz ao torque do motor são analisados e discutidos em função da rotação e da composição de combustível utilizado. / The present investigation explores the electronic management of internal combustion engines flex fuel, in which the focus is the development of a strategy for the spark advance angle as function of the abnormal combustion occurrence known ad Knock, in order to maximize the output torque. First, a method is developed for measuring the fuel composition and correction of the injection time and spark advance angle parameters through a fuel composition sensor. This parameter is defined through maps that work as an open loop system. Then, a method for detection of knock is developed, the peculiarities of the phenomenon are studied for different fuel compositions and the relationship of the phenomenon with the variation of the exhaust gas temperature and the engine output torque. Through the method of detection and the study of the phenomenon, an algorithm is developed to control the spark advance angle due to the knock occurrence, in which the approach allows the system to increase the angle when there is no occurrence of knock, but this additional angle is reduced when knock is detected. Engine management is performed through a development ECU model Flex-ECU, management algorithms are developed through the ASCET platform and data acquisition and calibration of and parameters is performed through a measurement and calibration platform. The result that the spark advance angle control brings to the engine torque output is analyzed and discussed depending on the rotation and the fuel composition used.

Dans un contexte de diminution des émissions polluantes émises par les moteurs à combustion interne, le secteur des transports assiste à une amélioration des motorisations mais également à une diversification des carburants pour l’automobile. L’utilisation de ces différents carburants entraîne souvent un impact sur les performances de la combustion. Dans le cas du moteur à allumage commandé, la performance dépend du dégagement d’énergie, image de la vitesse de la combustion, soit du front de flamme consommant le mélange air-carburant. Or toute flamme en expansion est théoriquement soumise à des effets de courbure et de cisaillement, toutes deux contributions de l’étirement. La réponse à l’étirement étant propre à chaque type de mélange air-carburant (lié au carburant proprement dit, à la richesse du mélange, à la dilution …), ce travail de thèse est centré sur la compréhension de l’impact de l’étirement sur les performances des carburants dans les moteurs à allumage commandé. Pour cela, différents mélanges air-carburant similaires du point de vue des propriétés thermodynamiques et des vitesses fondamentales de combustion laminaire mais avec des sensibilités à l’étirement différentes ont été sélectionnés. Ces mélanges ont ensuite été étudiés dans différentes configurations expérimentales et à l’aide de différentes techniques de mesure: moteur monocylindre opaque et à accès optiques, chambre sphérique de combustion turbulente. Les résultats montrent que les propriétés de sensibilités à l’étirement déterminées en régime laminaire comme la longueur de Markstein et le nombre de Lewis sont indicatrices du comportement des mélanges en combustion turbulente, comme dans la chambre de combustion caractéristique des moteurs à allumage commandé, et sont des paramètres à prendre en considération afin de prédire les performances plus globales de ces carburants que ce soit expérimentalement qu’en simulation. / In a context of decreasing pollutant emissions, the transport sector is facing an improvement of engine concept as well as a fuel diversification. The use of these different fuels often involves an impact on the combustion performance itself. In the case of Spark ignition engine, the efficiency is a function of the released heat, image of the combustion speed, i.e. the flame front speed consuming the air-fuel mixture. It is well known that every expanding flame is submitted to flame curvature and strain rate which are both contributors to flame stretch. As the answer of each air-fuel mixture (i.e. the fuel itself, the equivalence ratio, the dilution …) is different to flame stretch, the objective of this work is to understand flame stretch impact on fuel performance in Spark-Ignition engines. To achieve this goal, different fuel-air mixtures with similar unstretched laminar burning speed and thermodynamic properties but different responses to stretch were selected. Those mixtures were then studied with different experimental devices with different measurement techniques: single-cylinder metallic and optical engines, turbulent combustion spherical vessel. Results show that flame stretch sensitivity properties such as Markstein length and Lewis number, determined in laminar combustion regime, are relevant parameters to describe the flame propagation in turbulent combustion as in the combustion chamber of the Spark-Ignition engine and need to be taken into consideration to evaluate global performance of these fuels, experimentally and also in modeling simulation.

Le moteur à allumage commandé fortement downsizé est une des solutions les plus prometteuses utilisée par les constructeurs automobiles pour augmenter le rendement et réduire les émissions de CO2. Cependant, les conditions thermodynamiques plus sévères rencontrées dans ces moteurs favorisent l’apparition de combustions anormales (cliquetis et rumble) qui sont difficiles à analyser expérimentalement vu les risques encourus par le moteur. La méthode Reynolds Averaged Navier-Stokes (RANS) s’est imposée depuis plusieurs années pour l’étude des moteurs à piston dans l’industrie, mais elle n’est pas la plus appropriée pour étudier des phénomènes locaux et sporadiques comme les combustions anormales qui n’affectent pas le cycle moyen simulé en RANS. Grâce à l’utilisation d’un code compressible LES et au développement d’une version améliorée des modèles ECFM-LES (Extended Coherent Flame Model) et TKI (Tabulated Kinetics of Ignition) qui permet un découplage total entre les taux de réaction liés à la propagation de la flamme et à l’auto-inflammation, ces travaux mettent en évidence pour la première fois la capacité de la LES à décrire le phénomène de cliquetis dans une configuration réaliste d’un moteur à allumage commandé. Contrairement aux études précédentes [S. Fontanesi and S. Paltrinieri and A. D’Adamo and G. Cantore and C. Rutland, SAE Int. J. Fuels Lubr., 2013-01-1082, pp. 98-118][G. Lecocq, S. Richard, J.-B. Michel, L. Vervisch, Proc. Combust. Inst. 33 (2011) 3105-3114], une étude quantitative du cliquetis est réalisée grâce à des post-traitements spécifiques et similaires pour les résultats expérimentaux et numériques. La LES est capable de prédire la variabilité de la pression cylindre, la fréquence mais également l’angle moyen d’apparition de l’auto-inflammation sur un balayage d’avance à l’allumage. Une analyse 3D démontre également que le cliquetis se déclenche à différents endroits, mais principalement dans la moitié de la chambre sous les soupapes d’échappement. De plus, l’intensité du cliquetis est proportionnelle à la masse de gaz frais brûlée en auto-inflammation pour les faibles intensités, alors qu’une croissance beaucoup plus forte est observée pour les intensités les plus élevées. Ceci suggère que des facteurs supplémentaires interviennent comme la localisation du cliquetis ou les interactions entre l’acoustique interne et l’auto-inflammation. L’utilisation d’un code LES compressible permet une visualisation directe de ces interactions mettant en évidence que les faibles intensités sont liées à des auto-inflammations locales sans couplage alors qu’une transition de la déflagration vers la détonation est possible en moteur automobile et correspond aux intensités les plus fortes. / Highly boosted spark ignition engines are more and more attractive for car manufacturers in terms of efficiency and CO2 emissions reduction. However, thermodynamic conditions encountered in these engines promote the occurrence of abnormal combustions like knock or super-knock, which are experimentally difficult to analyze due to the risks of engine damages. The Reynolds Averaged Navier-Stokes (RANS) method mainly used in industry for piston engines is not the most appropriate as knock does not always affect the mean cycle captured by RANS. Using an accurate LES compressible code and improved versions of ECFM-LES (Extended Coherent Flame Model) and TKI (Tabulated Kinetics of Ignition) models allowing a full uncoupling of flame propagation and auto-ignition reaction rates, this work demonstrates for the first time that LES is able to describe quantitatively knocking combustion in a realistic downsized SI engine configuration. Contrary to previous studies [S. Fontanesi and S. Paltrinieri and A. D’Adamo and G. Cantore and C. Rutland, SAE Int. J. Fuels Lubr., 2013-01-1082, pp. 98-118][G. Lecocq, S. Richard, J.-B. Michel, L. Vervisch, Proc. Combust. Inst. 33 (2011) 3105-3114], a quantified knock analysis is conducted based on a specific post-processing of both numerical and experimental data. LES is able to predict the in-cylinder pressure variability, the knock occurrence frequency and the mean knock onset crank angle for several spark timings. A 3D analysis also demonstrates that knock occurs at random locations, mainly at the exhaust valves side. Knock intensity is found proportional to the fresh gases mass burned by auto-ignition at low knock intensities, while an exponential increase at the highest intensities suggests the influence of additional factors like the knock location in the cylinder or complex behavior of knocking combustion. A direct LES study of acoustic and autoignition interactions is then achieved. The LES visualizations allows showing that low knock intensities are only linked to local autoignition, but a deflagration to detonation transition occurs in such engine operating conditions and is responsible for the highest knock intensities.

The subject of this diploma thesis is the creation of a spark ignition thermodynamics model using pressure data measured on the actual engine. The model made in Matlab programming language combines Wiebe function for fuel energy release and Woschni correlation for heat transfer between in-cylinder gasses and cylinder walls. The created model contains compression and expansion stroke only, that's why are conditions at the start of compression and total heat addition calculated by measured pressure data from Skoda 1.0 MPI engine. Creation of transparent model by Matlab scripts enables other users to understand the basics of „zero-dimensional“ thermodynamics models properly, which are used by number of commercial solvers such as GT-Power simulation software. First part of this thesis deals with fundamental laws of heat addition and heat transfer, description of equations for its modelling and application. The major section is devoted to Matlab model, where defined input parameters are mentioned, description of model operation and model parameters influence study. Next parts develops issues of combustion pressure measurement and creation of engine simulation by GT-Power software used for comparison with Matlab model. In the thesis conclusion are simulations and actual engine data differences discussed.

No description available.

This work concerns a systematic study of IC engine operation with 100% biogas as fuel (as opposed to the dual-fuel mode) with particular emphasis on operational issues and the quest for high efficiency strategies. As a first step, a commercially available 1.2 kW genset engine is modified for biogas operation. The conventional premixing of air and biogas is compared with a new manifold injection strategy. The effect of biogas composition on engine performance is also studied. Results from the genset engine study indicate a very low overall efficiency of the system. This is mainly due to the very low compression ratio (4.5) of the engine. To gain further insight into factors that contribute to this low efficiency, thermodynamic engine simulations are conducted. Reasonable agreement with experiments is obtained after incorporating estimated combustion durations. Subsequently, the model is used as a tool to predict effect of different parameters such as compression ratio, spark timing and combustion durations on engine performance and efficiency. Simulations show that significant improvement in performance can be obtained at high compression ratios. As a step towards developing a more efficient system and based on insight obtained from simulations, a high compression ratio (9.2) engine is selected. This engine is coupled to a 3 kW alternator and operated on 100% biogas. Both strategies, i.e., premixing and manifold injection are implemented. The results show very high overall (chemical to electrical) efficiencies with a maximum value of 22% at 1.4 kW with the manifold injection strategy. The new manifold injection strategy proposed here is found to be clearly superior to the conventional premixing method. The main reasons are the higher volumetric efficiency (25% higher than that for the premixing mode of supply) and overall lean operation of the engine across the entire load range. Predictions show excellent agreement with measurements, enabling the model to be used as a tool for further study. Simulations suggest that a higher compression ratio (up to 13) and appropriate spark advance can lead to higher engine power output and efficiency.

For an engine running at a constant speed, both exhaust and intake processes are periodic in nature. This inspires the muffler designer to go for the much easier and faster frequency domain modeling. But analogous to electrical filter, as per Thevenin’s theorem, the acoustic filter or muffler requires prior knowledge of the load-independent source characteristics (acoustic pressure and internal impedance), corresponding to the open circuit voltage and internal impedance of an electrical source. Studies have shown that it is not feasible to evaluate these source characteristics making use of either the direct measurement method or the indirect evaluation method. Hence, prediction of the radiated exhaust or intake noise has been subject to trial and error. Making use of the fact that pressure perturbation in a duct is a superposition of the forward moving wave and the reflected wave, a simple hybrid approach has been proposed making use of an interrelationship between progressive wave variables of the linear acoustic theory and Riemann variables of the method of characteristics. Neglecting the effect of nonlinearities, reflection of the forward moving wave has been duly incorporated at the exhaust valve. The reflection co-efficient of the system downstream of the exhaust valve has been calculated by means of the transfer matrix method at each of the several harmonics of the engine firing frequency. This simplified approach can predict exhaust noise with or without muffler for a naturally aspirated, single cylinder engine. However, this proves to be inadequate in predicting the exhaust noise of multi-cylinder engines. Thus, estimation of radiated noise has met only limited success in this approach. Strictly speaking, unique source characteristics do not exist for an IC engine because of the associated non-linearity of the time-varying source. Yet, a designer would like to know the un-muffled noise level in order to assess the required insertion loss of a suitable muffler. As far as the analysis and design of a muffler is concerned, the linear frequency-domain analysis by means of the transfer matrix approach is most convenient and time saving. Therefore, from a practical point of view, it is very desirable to be able to evaluate source characteristics, even if grossly approximate. If somehow it were possible to parameterize the source characteristics of an engine in terms of basic engine parameters, then it would be possible to evaluate the un-muffled noise before a design is taken up as a first approximation. This aspect has been investigated in detail in this work. A finite-volume CFD (one dimensional) model has been used in conjunction with the two-load or multi-load method to evaluate the source characteristics at a point just downstream of the exhaust manifold for the exhaust system, and upstream of the air filter (dirty side) in the case of the intake system. These source characteristics have been extracted from the pressure time history calculated at that point using the electro-acoustic analogy. Systematic parametric studies have yielded approximate empirical expressions for the source characteristics of an engine in terms of the basic engine parameters like engine RPM, capacity (swept volume or displacement), air-fuel ratio, and the number of cylinders. The effect of other parameters has been found to be relatively insignificant. Unlike exhaust noise, the intake system noise of an automobile cannot be measured because of the proximity of the engine at the point of measurement. Besides, the intake side is associated with turbocharger (booster), intercooler, cooling fan, etc., which will make the measurement of the intake noise erroneous. From the noise radiation point of view, intake noise used to be considered to be a minor source of noise as compared to the exhaust noise. Therefore, very little has been done or reported on prediction of the intake noise as compared to the exhaust noise. But nowadays, with efficient exhaust mufflers, the un-muffled intake noise has become a contributing factor to the passenger compartment noise level as a luxury decisive factor. Therefore, in this investigation both the intake and the exhaust side source characteristics have been found out for the compression ignition as well as the spark ignition engines. Besides, in the case of compression ignition engines, typical turbocharged as well as naturally aspirated engines have been considered. One of the inputs to the time-domain simulation is the intake valve and exhaust valve lift histories as functions of crank angle. It is very cumbersome and time-consuming to measure and feed these data into the program. Sometimes, this data is not available or cannot be determined easily. So, a generalized formula for the valve lift has been developed by observing the valve lift curves of various engines. The maximum exhaust valve lift has been expressed as a function of the swept volume of the cylinder. This formulation is not intended for designing a cam profile; it is for the purpose of determining approximate thermodynamic quantities to help a muffler designer for an initial estimation. It has also been observed during the investigation that from the acoustic point of view, sometimes it is better to open the exhaust valve a little earlier, but very slowly and smoothly, and keep it open for a longer time. Although the exact source characteristics for an automobile engine cannot be determined precisely, yet the values of source characteristics calculated using this methodology have been shown to be reasonably good for approximate prediction of the un-muffled noise as well as insertion loss of a given muffler. The resultant empirical expressions for the source characteristics enable the potential user to make use of the frequency-domain cum-transfer matrix approach throughout; the time consuming time-domain simulation of the engine exhaust source is no longer necessary. Predictions of the un-muffled sound pressure level of automotive engines have been corroborated against measured values as the well as the full scale time-domain predictions making use of a finite-volume software.